There are occasions when it is desirable to give gasoline or other fuels from a given source a distinctive characteristic, a "label", such that it can be identified and distinguished from any similar fuel from other sources. Some such occasions arise in cases of suspected theft from a storage location. Other occasions involve investigations of intended or unintended commingling of similar fuels from different sources, or investigations of the path or time delay in distribution of fuels, as from refinery to customer. Still other occasions arise when spills or leaks of fuel of uncertain origin result in contamination of earth or water.
For short term problems involving relatively small volumes of fuel, such as suspected theft or studies of fuel distribution, dye-type tracer products are available and may be satisfactory. These include oil-soluble dyes of distinctive color and other oil-soluble products which impart little or no color to the fuel but can be extracted with a test reagent to which they impart a distinctive color. Fuel containing phenolphthalein for example produces a pink color in the water layer when shaken with an aqueous alkaline solution. However such dye-type tracers are expensive and are generally undesirable for long term or continued use in fuels.
It would be desirable, particularly when fuel spills or leakage may occur, to have available an inexpensive tracer material which could be added to all the fuel from a given source (i.e., marketing station, refinery, or company) on a continuing basis, without giving unwanted side effects. Then if a spill or leak releases fuel of unknown origin, as when gasoline found percolating through the earth may have come from any of several underground tanks or pipelines in the vicinity, a test for tracer in the recovered fuel would determine its source.
In selecting a suitable tracer, several factors must be taken into consideration. Among the major ones are: cost, ease of detection, stability, solubility and compatibility with the fuel, inertness to air, water and normal soil components, corrosivity, volatility and toxicity. Balancing all of these factors against each other, and after surveying many other types of compounds, I have found that the chlorohydrocarbons and chlorocarbons having at least 3 chlorine atoms and at least 2 carbon atoms per molecule, and having an atomic ratio of Cl/C of at least 1/3, appear to present an optimum combination of required properties.
Firstly, they are easily detectable in minute quantities by conventional gas chromatographic methods, using an electron capture detector. They can be selected according to boiling point so as to give a chromatogram peak readily distinguishable from the peaks resulting from other fuel components. Their boiling point can also be selected so as to fall within or above the upper 3/4 of the boiling range of the fuel, thereby minimizing evaporative loss of tracer from spills or leaks. They are suitably inert to air, water and soil components, as well as conventional fuel components, and they are non-corrosive. They are relatively non-toxic, as compared to compounds such as CCl.sub.4 and CHCl.sub.3. Finally, a considerable variety of suitable members are commercially available at low cost. No other class of compounds is presently known which meets all these qualifications.
According to one often desirable modification of the invention, two or more of the tracer compounds may be used in combination, thereby providing a highly distinctive gas chromatogram.